A new generation of optoelectronic devices such as organic photovoltaics (OPVs) and organic light-emitting transistors (OLETs) are fabricated using organic semiconductors as their active components. To be commercially relevant, these organic semiconductor-based devices should be processable in a cost-effective manner.
Bulk heterojunction (BHJ) solar cells commonly are considered the most promising OPV structures because they can be fabricated using roll-to-roll and large-scale production. BHJ solar cells include a photoactive layer disposed between an anode and a cathode, where the photoactive layer is composed of a blend film including a “donor” material and an “acceptor” material. FIG. 1 illustrates a representative BHJ organic solar cell structure.
State-of-the-art BHJ solar cells use fullerene-based compounds as the acceptor material. Typical fullerenes include C60 or C70 “bucky ball” compounds functionalized with solubilizing side chains, such as C60 [6,6]-phenyl-C61-butyric acid methyl ester (C60PCBM) or C70PCBM. The most common donor material used in BHJ solar cells is poly(3-hexylthiophene) (P3HT). However, P3HT/PCBM-based solar cells have several fundamental limitations. For example, the band-gap of P3HT is ˜2.0 eV, and it can absorb only a small portion (30%) of the solar spectrum.
Accordingly, the art desires new organic semiconductor materials for use in optoelectronic devices such as organic photovoltaics.